1. Field of the Invention
This invention relates to a process for producing polyolefins. More particularly, the invention is concerned with the homopolymerization or copolymerization of olefins which is effected in the presence of a catalyst system comprising the combination of an organometallic compound with a component resulting from the mutual contact of (i) an inorganic magnesium compound of a spherical shape having an average particle size of from 1 to 100 microns; (ii) a compound represented by the formula AlX.sub.3.OR'R" (where X represents a halogen atom, and R' and R" represent a hydrocarbon residual group having 1 to 20 carbon atoms; and (iii) a titanium compound represented by the formula Ti(OR).sub.4 (where R represents a hydrocarbon residual group having 1 to 20 carbon atoms).
2. Prior Art
In this field of technology, there are known a number of catalysts in which a compound of a transition metal such as titanium, vanadium and the like is carried on a solid inorganic magnesium compound such as magnesium halide, magnesium oxide, magnesium hydroxide and the like. Polymers obtained with use of such catalysts, however, are not satisfactory in that they differ in the shape of polymer particles, their bulk density is generally small, their powder fluidity is poor, and their particle size distribution is generally broad, on account of which the polymer contains a large portion of minute powder particles. Much therefore has been to be desired for improved productivity and slurry handling. When such conventional polymers are subjected to forming process, there often arise such problems as associated with dusts and declined efficiency and performance at the time of the molding or fabrication.
The present inventors already proposed in Japanese Patent Publication No. 51-13193 a catalyst system prepared by combining a catalyst component obtained by mixing and heating an inorganic magnesium compound, a compound represented by the formula AlX.sub.3.OR'R" (where X represents a halogen atom, and R' and R" respectively represent an alkyl group or aryl group having 1 to 4 carbon atoms) and a halogenated compound of titanium and/or vanadium, with an organoaluminum compound and/or an organozinc compound. As will be seen from comparative examples to appear later, it has been still difficult to eliminate the foregoing problems even with the use of the spherical inorganic magnesium compound of the present invention in place of the inorganic magnesium compound of the prior catalyst system.